This is the mineral Amphibole. Like many other rock-forming minerals, it belongs to the Silicate chemical family because it contains repeating chains of linked Silicon and Oxygen tetrahedra. With appropriate lighting Amphibole’s luster often appears vitreous, which means glassy. While it’s typically black, dark green or dark brown, it produces a white streak on a streak plate. Amphibole ranks between 5 and 6 on Mohs hardness scale. It exhibits oblique cleavage planes that intersect at about 120 degrees. Since many different varieties of Amphibole exist, specific gravities range between 2.9 and 3.6. Several varieties of Amphibole are classified are Asbestos. Asbestos is an umbrella term for 6 specific minerals, all of which have thin, fibrous, thread-like properties and are resistant to heat, electricity, and corrosion. While practical, these properties also create health threats, including lung scarring and lung cancer. As a result, several dozen countries around the world have banned the use of Asbestos. Today we mainly use the mineral Amphibole when it’s part of the metamorphic rock Amphibolite. This black, coarsely grained rock is especially durable and is often used to support railroad lines and build roads. Polished Amphibolite produces a distinctive black shine and is often used in small applications like jewelry, and larger applications like countertops, paving stones, and building facades.